Your Ipad is not infected, but the virus can change the settings on your router. Are there other computers in your house? It might be that another computer got infected, the settings on your router got changed and your ipad is getting the bad dns servers from your router.
The message you got is legit. Google announced they would notify people here: http://googleonlinesecurity.blogspot.com/2012/05/notifying-users-affected-by-dns changer.html Go search news.google.com for DNS changer. Your ISP may also have been trying to notify you over the last few months as well.
Check the DNS server settings on your router. If you find the DNS servers on your router have been changed to the bad ones, change them to something you trust (your ISP's, Google's etc) and then change the password on your router. If there are other computers in your house, check those as well - you might have a pc that is the source of the infection. Make sure your router is secured so only you can get on it, not your neighbors.
Here is a list of the bad DNS Servers:
85.255.112.0 through 85.255.127.255
67.210.0.0 through 67.210.15.255
93.188.160.0 through 93.188.167.255
77.67.83.0 through 77.67.83.255
213.109.64.0 through 213.109.79.255
64.28.176.0 through 64.28.191.255
To make the comparison between the computer’s DNS servers and this table easier, start by comparing the first number before the first dot. For example, if your DNS servers do not start with 85, 67, 93, 77, 213, or 64, you can move on to the next step. If your servers start with any of those numbers, continue the comparison.